In a known power storage apparatus, power storage modules are connected, and a common control device (also called the main controller where appropriate) is provided for the power storage modules. Each of the power storage modules has a module controller, and communication is performed between the module controller and the main controller via a communication channel.
So as to monitor the condition of a power storage unit and detect malfunction, the module controller includes a monitoring circuit and a microcomputer (also called the sub micro-controller unit where appropriate). The power storage unit is formed with series-connected sub modules, for example. The monitoring circuit monitors the voltages of the respective sub modules, compares the voltages of the respective sub modules with a predetermined threshold value using a comparator, and outputs detection signals (1-bit detection signals, for example) indicating normality/abnormality.
At a time of charging, the voltage of each sub module is compared with a predetermined value, and a detection signal indicating whether the voltage is an overvoltage (also referred to as OV where appropriate) is generated. At a time of discharging, the voltage of each sub module is compared with a predetermined value, and a detection signal indicating whether the voltage is an undervoltage (also referred to as UV where appropriate) is generated. At a time of charging/discharging, the value of the current flowing in the sub modules is compared with a predetermined value, and a detection signal indicating whether the current is an overcurrent (also referred to as OC where appropriate) is generated. Further, at a time of charging/discharging, the temperature of each sub module is compared with a predetermined value, and a detection signal indicating whether the temperature is an overtemperature (also referred to as OT where appropriate) is generated.
Further, when a power storage module is charged, the voltages and the currents of the respective sub modules are supplied to the sub micro-controller unit of each module, and balance adjustment is performed to equalize the voltages of the sub modules. Without the balance adjustment, some of the sub modules will not be sufficiently charged due to variation among the sub modules.
For the balance adjustment, the above described detection signals from the monitoring circuit are supplied to the sub micro-controller unit. Further, the detection signals are transferred from the module controller to the microcomputer (also called the main micro-controller unit where appropriate) of the main controller via a communication channel. The main controller receives detection signals from the respective power storage modules, and controls charging/discharging operations.
For example, according to Patent Document 1 mentioned below, when there is a sub module that has a voltage difference from the highest voltage detected from sub modules (cell blocks) within a discharging voltage range, charging is temporarily stopped, and the sub module as well as the sub module having the highest voltage is made to discharge, to update the highest voltage after the discharging. The cell balance adjustment is repeated until the voltage difference between the highest voltage and the lowest voltage falls within a predetermined voltage range, so that the time required for cell balance control can be shortened, according to Patent Document 1.